Knocking on drivers side floor after exhaust

[96 Dynamite]

Hey guys not sure if this is in the right area but since having a Flowmaster hi flow cat with y pipe installed by a local exhaust shop I've noticed a "knocking" on the driver side kind of near to where the pedals are. It only on acceleration and hitting bumps which lead me to think the headers were not tight to the system but I see no leaks or loosness and the bolts are tightened to the max. I've spent a half hr laying under it wiggling stuff around to no avail. Anyone have any ideas?

 

[tommyboi87]

Got any heat shields under there?

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[96 Dynamite]

Yeah it does and that might be it. The one under the master cylinder is tight but the one under the drivers side header is a little loose and really close to the headers.